1. Field of the Invention
The present invention relates generally to methods of selectively reducing the water permeabilities of subterranean formations, and more particularly, to improved methods of reducing the production of salt water from wells which produce both oil and salt water.
2. Description of the Prior Art
A problem often encountered in the production of oil from oil-bearing formations or zones is the simultaneous production of salt water. While the oil well is usually completed in an oil-bearing zone, when there is a salt water bearing zone adjacent the oil zone, the higher mobility of the salt water often allows it to flow into the oil zone by way of natural fractures and high permeability streaks. In the production of such wells, the ratio of salt water to oil recovered often becomes so high that the cost of producing the salt water, separating the salt water from the produced oil and disposing of the salt water represents a significant economic loss.
In order to reduce the production of salt water from such wells, viscous aqueous polymer solutions have been utilized heretofore. That is, an aqueous polymer solution is pumped into the oil zone so that it enters the salt water zone communicated therewith. The polymer solution is then crosslinked whereby a stiff gel is formed which plugs the natural fractures and high permeability streaks through which salt water flows from the water zone to the oil zone.
While the use of aqueous polymer solutions for reducing the production of salt water has achieved varying degrees of success, the lack of strength of a crosslinked polymer will cause it to deteriorate over time and to be produced back out of the well with salt water produced therefrom. The presence of the polymer in the salt water results in the water becoming contaminated with bacteria which in turn causes corrosion of tubular goods and other problems in salt water disposal wells.
Because a salt water reduction treatment using an aqueous polymer solution requires that a relatively large volume of the aqueous polymer solution be pumped into the producing formation, the permeability of the oil zone is often reduced. If an oil production stimulation treatment is subsequently carried out in the oil zone, the production of polymer with the oil and water produced is increased. Additionally, the oil produced from an aqueous polymer solution treated well usually can not be pumped in that the increased pressure drop at the well bore causes the deterioration of the crosslinked polymer and its production with the produced oil and salt water.
The relatively large volume of aqueous polymer solution required for performing the heretofore used polymer water reduction treatments cause the treatments to be very expensive.
Thus, there is a need for an improved method of selectively reducing the water permeability of a subterranean oil-bearing formation without incurring the above mentioned problems and high cost.